The present invention relates to compositions comprising blends of resins. More particularly it relates to compositions comprising blends of aromatic polycarbonate resins, graft derivatives of ethylene-propylene-diene terpolymers, and an amount of a multiphase composite interpolymer comprising a crosslinked acrylic first stage which also contains graftlinking monomer and a final rigid thermoplastic phase which is effective to improve the resistance to environmental stress crazing and cracking of said blends.
The polycarbonates are well known commercially available materials which, due to their many advantageous properties, find use as thermoplastic engineering materials. The polycarbonates exhibit, for example, excellent properties of toughness and heat resistance.
However, the polycarbonates are generally susceptible to environmental stress crazing and cracking. Environmental stress crazing and cracking refer to the type of failure which is hastened by the presence of organic solvents such as, for example, gasoline, acetone, heptane and carbon tetrachloride when such solvents are in contact with stressed parts fabricated from aromatic polycarbonate resins. The most significant effect is a loss in impact strength and an increase in brittle type failure.
Polycarbonate resins have been blended with other thermoplastic materials such as high molecular weight polymeric glycol esters of terephthalic and/or isophthalic acid and acrylonitrile-butadiene-styrene resins (ABS resins). Mixtures of polycarbonates with ABS graft copolymers are disclosed to have improved impact properties in U.S. Pat. No. 4,172,103. However, it is disclosed in U.S. Pat. Nos. 3,130,177 and 3,825,292 that the impact resistance of polycarbonate resins tends to be lowered when they are blended with ABS resins.
Thus, the blending art, particularly when dealing with polycarbonates, is a generally complex and somewhat unpredictable area where the empirical approach is still generally the rule rather than the exception. Thus, in order to provide useful binary blends of a polycarbonate resin with another resin, the two resins must be compatible to a certain degree, combinable over certain useful concentrations, and the blends should exhibit a combination of the various advantageous properties of the resins rather than the individual properties of the neat resins. The formulation of blends containing three or more different resins is fraught with a much higher degree of complexity and unpredictability.
Grafted derivatives of ethylene-propylenediene terpolymers and compositions of such polymers with other resins are known in the art and are described in the patent literature. It has been disclosed, for example, that olefinic copolymers and terpolymers can be grafted with styrene, acrylo-nitrile-styrene, methyl methacrylate, styrene-methyl methacrylate, and the like, to provide thermoplastics which can be further blended, e.g., with styrene-acrylonitrile, and molded, extruded, or vacuum formed into articles having good tensile and impact strengths.
Polymers of this type and methods for their preparation are described in U.S. Pat. Nos. 4,202,948 and 4,166,081, the former being incorporated by reference. Thermoplastic resin blends of polysulfone resins and graft derivatives of ethylene-propylene-diene terpolymers are disclosed in U.S. Pat. No. 3,641,207 to have good processability and impact resistance over relatively narrow concentration ranges.
Aromatic polycarbonate resins and grafted derivatives of ethylene-propylene-diene terpolymers are combinable with each other over a wide range of concentrations and provide compositions which exhibit advantageous properties after molding. Such properties are obtainable over a wide range of compositions. Especially noteworthy properties are high gloss on the surface of articles molded from these compositions and improved resistance to environmental stress crazing and cracking as compared with aromatic polycarbonate resins.
While these blends of polycarbonate resin and graft derivatives of ethylene-propylene diene terpolymers are useful in a wide variety of applications there exist certain situations which require better resistance to environmental stress crazing and cracking than possessed by these blends. It is, therefore, an object of the instant invention to provide compositions containing blends of polycarbonate/grafted derivative of ethylene-propylene-diene terpolymer which possess improved resistance to environmental stress crazing and cracking.